In the 3rd Generation Partnership Project Radio Access Network, Radio layer 2 and Radio layer 3 radio resources (RAN2) working groups, an uplink Hybrid Automatic Repeat Request (HARQ) entity is conceptually in charge of co-ordinating user equipment (UE) operation in order to provide data for uplink transmission as appropriate. At each transmission opportunity, the uplink HARQ process associated with that transmission opportunity may be instructed by the uplink HARQ entity to perform various actions, including a new data transmission, adaptive retransmission, non-adaptive retransmission or nothing.
An adaptive retransmission allows for different physical resources or parameters, signaled through downlink control information than for the most recent transmission of the same transport block. Conversely, non-adaptive retransmission is performed using the same physical resources as the most recent transmission for the same transport block but with a different redundancy version. New data transmissions and adaptive retransmissions have priority over non-adaptive retransmissions for the same transmission opportunity.
For adaptive retransmission, the Downlink Control Information (DCI) format 0 (DCI 0) is used to signal the retransmission. In some cases and for various reasons the UE may see a DCI 0 ordered adaptive retransmission where the transport block size has changed without a New Data Indicator (NDI) flag having been changed. This may be caused, for example, by a UE failing to detect a DCI 0 on the physical downlink control channel (PDCCH) which was transmitted by the Evolved Node B (eNB). Such missed detection is termed a false negative, and may occur due to poor or changing channel conditions, sudden interference and other variable conditions typically associated with wireless transmission channels. Further, the UE may, from time to time, detect a DCI 0 on the PDCCH which is not actually representative of a DCI 0 that was transmitted from the eNB. Such detection is termed a false positive and may interfere with normal UE operation.
Thus, in some situations, a UE may detect a DCI 0 addressed to the UE with a non-toggled NDI and with a different transport block size.